1. Field of the Invention
The present invention relates to an image heating device for an electrophotographic image forming apparatus such as a copying machine, printer, or facsimile.
2. Description of the Related Art
A method of fixing an unfixed toner image onto a sheet (recording material) in an image forming apparatus, which is conventionally adopted, is a thermal fixing method wherein the toner image which is not yet fixed on the sheet is heated and melted to be thereby fixed onto the sheet because of its favorable stability and fixability.
When the sheet is fixed in a fixing region according to the fixing method, a temperature distribution on a surface of a heating material which transits a sheet-transit region is substantially even.
In the case where small-size sheets each having a width smaller than that of a largest-size sheet are continuously fixed in the fixing region, however, a temperature on the surface of the heating material in a non-sheet-transit region is excessively increased. The temperature increase occurs because, when the small-size sheets are continuously fed, heat is accumulated in a part of the non-sheet-transit region since the heat is not removed by the sheet in the non-sheet-transit region where the sheets do not transit. The phenomenon is called the temperature increase in the non-sheet-transit region (end-portion temperature increase) in an image heating device. When the temperature in the non-sheet-transit region reaches a high temperature, the temperature of the heating material exceeds a temperature-increase limit, which possibly causes damages.
Japanese Patent Applications Laid-Open (JP-A) No. 04-51179 recites the technology, wherein, in order to prevent the temperature increase in the non-sheet-transit region thus described, a cooling fan is provided in the image heating device so as to send air to the non-sheet-transit region of the heating material, so that the temperature increase is controlled. According to the technology recited in JP-A No. 04-51179, the cooling fan provided in the image heating device sends air selectively to a side where the non-sheet-transit region is provided.
In the technology recited in JP-A No. 04-51179, as shown in FIG. 9, air Z1 from a cooling air fan 1A collides with a fixing belt 20A and is thereafter split into air Z2 which is sent upward (downstream in a conveying direction) and air Z3 which is sent downward (upstream in the conveying direction). Accordingly, longitudinal ends of the fixing belt (heating film) 20A in an image heating device 101A are cooled down. However, the upward air Z2 is retained above the image heating device 101A, which excessively increases temperatures of a conveying guide 104A and a conveying roller 105A. As a result, problems are generated in the conveying process.